Senator Bernie Sanders and former Secretary of State Hillary Clinton shake hands during the Democratic Debate on October 13, 2015. (Photo: Getty)Bernie Sanders' stature and strength continues to grow. He is the folk hero of the primary season. His message is repeated consistently to millions of people. He's neck and neck with Hillary in early primaries. The money is rolling in, and the volunteers have become a genuine mass movement. A sense of humor has emerged from under the early strains.

Most important to many left-progressives is the rational discussion of democratic socialism for the first time in 90 years, since we last had an elected bloc of socialist mayors agitating for what became the New Deal.

The foam-at-the-mouth Republicans help Bernie seem sensible by comparison. The Denmark comparisons haven't hurt him that much, because as the candidate himself says, a majority of Americans agree with him on everything from expanded Medicaid to taxes to overturning Citizens' United.

The challenge Bernie faces ahead lies in the fact that Denmark is about as white as Vermont. (94-95 percent of Denmark is white including a percentage of its immigrants while 95 percent of Vermont is white also.) Early Democratic primary states, New Hampshire and Iowa, are about as white as it gets.

The Democratic primaries are all about people of color: Latinos, African-Americans, Asian -Americans and women of all colors. The progressive bloc of environmentalists and peace forces are far smaller. Loyalties to Hillary Clinton are deep; for example, in 2008 she won Latinos by two-to-one against Barack Obama.

It almost certainly won't work for the Sanders campaign to claim that he's the "best' candidate for people of color or feminists. He'll have to do what Obama did in 2008 when black voters turned away from Hillary when Obama did so well in white Iowa on his opposition to Iraq. How could Bernie switch black and brown voters away from Hillary by showing he can win the argument over Wall Street? Other than her suffering a meltdown over a scandal or gaffe, it doesn't seem plausible.

This is the classic dilemma of the Left dating back one hundred years - class analysis against a race and gender analysis. Echoes already are showing up in Vermont where Bernie sympathies with white gun owners while Hillary, massacre victims and black people are seething against the NRA.

Or take South Carolina, the citadel of failed populism, where the black primary electorate might be fifty-five percent and white progressives are limited to university towns. With their right to vote on the line, will many blacks vote for Bernie? Will Rep. Jim Clyburn, the former leader of the Orangeburg State student movement and now the third-ranking Democrat in the House, jump to Bernie? Impossible.

Overall, African-Americans are 87 percent Democratic, Latinos are 61 percent (2012 data) with 96 percent of black women and 76 percent of Latinas having voted for Obama. By contrast, about 56% of white women voted for Bush, McCain and Mitt Romney. So where is Bernie's base? Besides a sliver of black and brown votes, that leaves him looking at white independents. Even if he splits the Jewish vote with Hillary, that’s 1.5 percent nationally. In his soul, is that what he really wants?

There must be a plan B (for Bernie), starting now through the primaries, through the platform debates, and through what might be another very close national election. Bernie and his new history-making force must be looking hard at all their moves down the road.